The present invention relates to pipelines in general, and more particularly to improvements in pipelines which can be used to convey compressed gaseous fluids and are assembled of two or more tubular components or members. The invention further relates to a method of assembling the components of a pipeline.
German patent application No. 34 23 952.9 discloses a pipeline wherein one (first) end portion of a first tubular member is inserted into one (second) end portion of a second tubular member. The internal surface of the second end portion has a circumferentially complete groove for a ring of soft elastomeric material (e.g., rubber or an elastic plastic substance) which is caused to sealingly engage the first and second end portions so that these end portions can be welded to each other as soon as the ring is caused to undergo deformation which is required to establish a satisfactory seal with each of the two end portions. This renders it possible to weld the first and second end portions to each other while the respective tubular members convey a compressed gaseous fluid. As a rule, the welding operation involves the application of an annular weld or seam along the end face of the second end portion.
The ring has two annular sealing lips including an outer and an inner lip, as considered in the radial direction of the groove. The inner lip is acted upon by compressed gaseous fluid in the pipeline and is thereby maintained in sealing engagement with the external surface of the first end portion. The outer lip is also deformed by the compressed gaseous fluid in the pipeline and is thereby biased against the (bottom) surface in the radially outermost portion of the groove. In other words, the inner lip is biased radially inwardly (against the first end portion) and the outer lip is biased radially outwardly (against the second end portion). The two lips face away from the free end of the second end portion, i.e., in a direction such that they can be acted upon and deformed by compressed gaseous fluid in the pipeline. The flow of compressed gaseous fluid through the pipeline is interrupted during insertion of the first end portion into the second end portion (at such time, the sealing ring in the internal groove of the second end portion slides along the external surface of the first end portion and/or vice versa). The admission of compressed gaseous fluid into the pipeline is resumed as soon as the insertion of the first end portion into the second end portion is completed so that the fluid can deform the two lips in the aforedescribed manner. The ring then prevents leakage of the compressed gaseous fluid and allows for the application of an annular weld while the pressure in the pipeline exceeds the pressure in the surrounding atmosphere. The pressure of gaseous fluid must suffice to ensure that the inner lip is held in a requisite sealing engagement with the external surface of the first end portion (the gaseous fluid acts upon the outer side of the inner lip), and that the outer lip is held in requisite sealing engagement with the bottom surface in the groove of the second end portion (the gaseous fluid acts upon the inner side of the outer lip). The inner diameter of the ring and the diameters of the lips thereon must be selected in dependency on the inner diameter of the second end portion, on the outer diameter of the first end portion and on the diameter of the bottom surface in the radially outermost portion of the groove. The inner diameter of the ring and the inner diameter of the inner lip cannot be reduced below a certain value because this would prevent the first end portion from entering the second end portion while the ring is installed in the internal groove of the second end portion. On the other hand, the selection of a small inner diameter for the ring and for its inner lip would enhance the sealing action of the ring, particularly between the inner lip and the external surface of the first end portion. Moreover, the sealing action of the ring is dependent practically exclusively upon its weakest parts i.e., upon the two lips, because one of the lips is used to sealingly engage the first end portion and the other lip is caused to sealingly engage the second end portion. Still further, it is rather difficult to ascertain whether or not the lips of the ring are in proper positions for the establishment of satisfactory seals when the insertion of the first end portion into the second end portion is completed.